In U.S. Pat. No. 3,911,093 to F. G. Sherif et al., a process for reacting SO.sub.2 and H.sub.2 S in an aqueous phosphate absorbent is described in which elemental sulfur is produced. The molarity for the phosphate buffer is said to range from 0.5-2.0 with an exemplification of a maximum of 1.5 molar. The pH range is given as 2.5 to 5, preferably 2.8 to 4.5.